When cutting plastic columns and, particularly, columns used for the production of catalytic converters, it is essential that the cutting wire be guided in such a manner that the resulting cut edges of the column are as neat as possible. Since columns used for the production of catalytic converters are typically in the form of plastic webs (i.e., prior to curing to a hardened state), it is also important that, when cut, the columns are not crushed. Moreover, one feature which all successful column cutting devices must have is the capability of replacing cutting wires worn and/or damaged due to repeated cutting operations.
Devices which cut columnar articles are known, the most common of which cut the column either by means of horizontally strung wire(s) which may be passed vertically through the column, or by means of vertically strung wire(s) which may be passed horizontally through the column.
In German Offenlegungsschrift No. 2,353,085, a cutting device is described having a cutting wire fixed at both of its ends to the lateral strut of a vertically movable U-shaped frame. The cutting wire is tensioned outside the space reserved for the passage of the column by means of a tensioning device extended between an upper cross-bar of the frame and the cutting wire. The tensioning device thus exerts tension on the cutting wire at a location between the fixed ends of the wire so that the wire forms an angle with respect to an imaginary line extending between the wire's fixed ends.
A cutting device having multiple cutting wires held by a pivotally movable frame is disclosed in German Auslegeschrift No. 2,220,360. The cutting wires thus pivot in a downward direction so as to cut a column.
A cutting device is also described in German Offenlegungsschrift No. 1,584,496 wherein the cutting wires are strung horizontally between a pair of offset circular rings. The offset rings are mounted for rotation about respective parallel axes such that only one of the rings encompasses a column to be cut. Synchronous rotation of the two circular rings thus causes the cutting wires to pass vertically through the column (which moves parallel to the rotational axes of the rings) thereby cutting the same.
Cutting wires radially extending from the center of a circular ring-type wire guide are disclosed in German Auslegeschrift No. 2,100,819. The wire guide encloses a column to be cut while a support for the column is positioned laterally to the guide's rotational axis. The cutting wires are cleaned by means of wipers associated with each wire--the wipers being retained in a circular guideway whose center is offset relative to the rotational axis of the circular wire guide. Thus, upon rotation of the wire guide, each wiper will move circularly within the wiper guideway and, due to the off-center relationship between the wiper guideway and the wire guide, each wiper will also move longitudinally along its respective wire thereby cleaning the same.
All of these known cutting devices, however, are disadvantageous in that the movement of the cutting wire follows a vertical (or almost vertical) path relative to the column at the point of contact between the cutting wire(s) and the column. Thus, when used to cut uncured ceramic Web-type columns (such as those employed in the production of catalytic converters), such unidirectional movement of the cutting wire tends to cause the column to be crushed at the point of contact between the wire and the column thereby leading not only to imperfect or unacceptable cuts in the column, but also to premature wear of the cutting wires--i.e., the same section(s) of wire will repeatedly be exposed to abrasive wear. Another disadvantage which all these known devices have in common is that the worn wires can only be replenished by time-consuming procedures whereby the existing worn wires are physically removed and new wires are replaced. This obviously results in equipment down time and loss of production with the concomitant economic losses associated therewith.
According to the present invention, however, method and apparatus for cutting columnar articles (for example, plastic web-type columns typically employed in the production of catalytic converters) are provided whereby such columns may be cut along a predetermined plane (e.g., a plane transverse to the column's length) utilizing at least one cutting wire tensioned between a pair of spaced-apart locations situated to the exterior side of the column to be cut. Orbital movement of one of such locations, according to this invention, causes the wire to cut the column and, during such orbital movement, the length of the wire (i.e., situated between such locations) is simultaneously continually varied so as to achieve a beneficial reciprocal rectilinear (e.g., "saw-type") cutting action.
The present invention thus achieves bidirectional movement of the cutting wire--that is, the cutting wire is moved generally in a planar path through the column to be cut while also continually rectilinearly moving within such plane. This beneficial bidirectional cutting action of the present invention minimizes deformation of the column being cut since the "saw-type" cutting motion and movement of the cutting wire in a planar cutting path more easily accomplish cutting of the column as compared to undirectional cutting devices of the prior art. Moreover, since the length of the cutting wire is continually varied during the cutting operation, wear on the wire is more evenly distributed along its length thereby prolonging its useful life.
In a preferred form of the invention, the cutting wire is tensioned between a pair of spaced locations, which may be embodied in supply and take-up spools for the wire, respectively. One of the spools (e.g., the take-up spool) is mounted on an orbitally movable circular ring, while the other spool (e.g., the supply spool) is in a fixed-position relative to the column to be cut. Thus, as the movable spool is moved in its orbit around the column to be cut, the length of the wire will be continually varied due to the wire being "paid out" from the other spool. That is, during one segment of such orbital movement, the length of the wire between the two spools will vary between a shorter length L.sub.l to a longer length L.sub.2 and then, during another segment of such orbital movement, the cutting wire length will return to length L.sub.l from length L.sub.2.
The circular ring can be driven by any suitable means. Preferably, the ring is driven by means of a pinion gear intermeshed with the circular ring and operatively connected to a suitable power source (e.g., an electric motor).
It is also possible to incrementally advance the wire from the supply reel to the take-up reel at periodic intervals (e.g., once per cutting cycle). In this way, incremental lengths of "fresh" wire are constantly being supplied to the actual cutting area thus eliminating the need to shut down the production line while a worn cutting wire is replaced.
Other aspects and advantages of this invention will become more clear to the reader after careful consideration is given to the detailed description of the preferred exemplary embodiments thereof which follow.